1. Field of the Invention
The present invention relates to polymer compositions and to their films. Particularly, the invention relates to polymer compositions from which films superior in low-temperature heat sealability, hot tack property and transparency can be produced and also relates to their films. In addition, the invention relates to polymer compositions from which films superior in low-temperature heat sealability, hot tack property and transparency can be obtained and which exhibit less tackiness when being fabricated into films and the invention also relates to their films.
2. Description of the Related Art
Films or sheets obtained by shaping polypropylene have been used widely in the field, particularly, of packaging of foods or the like due to their superior transparency, heat resistance, food sanitation and the like.
JP-A-55-59964 discloses a film that has a lowered heat seal temperature and an increased heat seal strength and that is not affected with respect to other properties films are required to possess. Specifically disclosed is a polypropylene multilayer film in which a layer of a mixture composed of from 85 to 97 parts by weight of a propylene-butene-1 copolymer having a butene-1 content of from 10 to 25% by weight and from 3 to 15 parts by weight of a propylene-butene-1 copolymer having a butene-1 content of from 80 to 93%.
JP-A-61-108647 discloses a crystalline propylene random copolymer composition from which a polypropylene composite laminate superior in low-temperature heat sealability and heat seal strength can be obtained. Specifically disclosed is a crystalline propylene random copolymer composition comprising a crystalline propylene random copolymer which is made up of propylene and α-olefin other than propylene and which contains the propylene as a main component and a 1-butene random copolymer made up of ethylene and 1-butene.
In recent years, in the field of packaging of foods and the like, the fabrication speed of bags has been increased and a material which can be processed at an increased fabrication speed is awaited. For the propylene copolymer compositions, a further improvement in low-temperature heat sealability, hot tack property and transparency of films obtained from the compositions is awaited. Moreover, an improvement in tackiness of the compositions during film formation is also awaited.